Inter-vehicle wireless communication has the potential to considerably improve vehicle safety. Warning information such as emergency electronic brake light signaling, road condition warnings, or accident warnings can be transmitted directly to adjacent vehicles or passed on to more distant vehicles. The inherent broadcast nature of radio communication lends itself to multicast multi-hop implementations for vehicle safety. Cooperative collision warning or avoidance can be achieved through periodic multicast of vehicle vector information. A number of traffic safety forums such as the Vehicle Safety Communications Consortium (VSCC), the Federal Highway Administration (US DOT FHWA), and ISO (TC204 WG16) have identified high priority applications or scenarios based on injury or fatality statistics for example.
Ad hoc inter-vehicle communication has several advantages over infrastructure or cellular-based telematics communication methods including: (i) low latency communication, (ii) robustness due to multiple transmitter/forwarder or mesh topology, (iii) low cost unlicensed frequency band use, (iv) carrier independence, and (v) larger capacity due to spatial diversity and availability wherever equipped vehicles are. The coverage, robustness and latency benefits are particularly important, if not uniquely important, for safety applications.
However, mobile ad hoc networks present particular challenges including (a) routing, whether unicast or multicast, in dynamic topologies, (b) contention avoidance and (c) synchronization without a centralized synchronization and access management function, and (d) retaining low latency over relatively long distance multi-hop packet routes. High densities of vehicles present particular challenges for synchronization and contention management while low densities of vehicles present particular challenges for routing. Latency challenges exist both in sparse networks and dense networks. Sparse networks present latency issues due to indirect routing or fragmented networks. High-density networks also present latency concerns due to contention and shared bandwidth for multiple applications. The performance of inter-vehicle networks under low and high traffic density of equipped vehicles will determine the feasibility of such systems and is a critical concern due to the long time-frame required to reach critical mass and maturity.
Therefore, it is desirable to provide an inter-vehicle communication approach that addresses these and other challenges associated with such systems.